Germ & dormancy - generic practical

Improving the identification, handling
and storage of “difficult” seeds
Supported by
Germination / dormancy Practical Exercise
Introduction
Physiological and physical dormancy are the two most important constraints to the
successful germination testing of conservation collections. Disruption of the covering
structures surrounding seeds and fruits can be a very effective means of overcoming
both forms of dormancy. However, there are important differences in the way the
treatment is performed:
Physical dormancy: The most effective way to treat small samples of seeds is to nip
(chip) or file a small portion of seed coat to enable water uptake. Care is taken to
position the treatment away from the underlying embryo to avoid damage.
Physiological dormancy: Seeds with physiological dormancy often fail to germinate
because the embryo does not have the growth potential to break through the covering
structures. To alleviate this constraint, a portion of seed / fruit coat is carefully
removed close to the embryo.
Chemicals such as nitrate and gibberellins can also be effective in removing
physiological dormancy. However, the effects of these and other germination
promoters can be very dependent on the concentration used and method of
application. For example, continuous exposure to GA during a germination test can
result in weak, elongated seedlings that would be difficult to establish if they were
required for regeneration.
Objective
After this practical you will understand the important differences between
scarification treatments to overcome physical dormancy and surgical treatments aimed
at removing the constraint to embryo growth when seeds have physiological
dormancy. You will also understand that seed responses to promoting factors such as
gibberellins are dependent on concentration and method of application.
You will also learn the importance of the ‘cut test’ in the evaluation of ungerminated
seeds at the end of germination tests.
Materials
• Seeds of physically dormant species eg Corchorus sp, Abelmoschus esculentus,
• Seeds of physiologically dormant species eg Cleome gynandra, wild sorghum,
Eragrostis pallens, Panicum coloratum, Vernonia galamensis
• Potassium nitrate
• Gibberellic acid (GA)
• Appropriate germination media, eg 1% water agar, paper, sand
• Petri dishes
Also supported by

Improving the identification, handling
and storage of “difficult” seeds
• Forceps
• Scalpel
Method/Procedure
Depending on time, species available and the particular dormancy issues you want to
better understand, the following treatments may be tried.
1. GA experiment
Draw three samples of 40 seeds each of a physiologically dormant species. Subdivide
each sample into four replicates of ten seeds. Sow the first, second and third set of
replicates on 1% water agar containing 0mM, 0.7mM and 10mM GA respectively (or
on paper wetted with GA solutions) and incubate at 25 o C. Score for germination after
7 – 8 days of incubation. Use protrusion of the radicle as measure of germination.
2. Requirement for alternating temperature
Draw two samples of 40 seeds each of a physiologically dormant species. Subdivide
each sample into four replicates of ten seeds. Sow the first and the second set of
replicates on appropriate media and incubate at 25 o C and 30/25 o C respectively. Score
for germination after 7 – 8 days of incubation. Use protrusion of the radicle as
measure of germination.
3. Surgical treatment
Draw three samples of 40 seeds each of a physiologically dormant species. Subdivide
each sample into four replicates of ten seeds. Surgically expose the embryo of the
seeds of the second set of replicates carefully to avoid damaging the embryo. Nip
away from embryo, the seed coat of the seeds of the third set of replicates Sow the
three sets of replicates on on appropriate media and incubate at 35/15 o C. Score for
germination after 7 – 8 days of incubation. Use protrusion of the radicle as measure of
germination.
4. Nipping experiment
Draw two samples of 40 seeds each of a physically dormant species. Subdivide each
sample into four replicates of ten seeds. Nip away from the embryo, the seed coat of
the seeds of the second set of replicates to avoid damaging the embryo. Sow both the
first and second set of replicates on on appropriate media and incubate at 25 o C. Score
for germination after 7 – 8 days of incubation. Use protrusion of the radicle as
measure of germination.
5. Potassium nitrate treatment
Draw two samples of 40 seeds each of a physiologically dormant species.. Subdivide
each sample into four replicates of ten seeds. Sow the first and second set of replicates
on 1% water agar containing 0% and 0.2% Potassium nitrate (or on paper wetted with
0.2% nitrate solution) respectively and incubate at 25 o C. Score for germination after 7
– 8 days of incubation. Use protrusion of the radicle as measure of germination.
Supported by
Also supported by

Improving the identification, handling
and storage of “difficult” seeds
6. Physical Scarification
Scarify physically dormant legume seeds by rubbing the seeds on sand paper avoiding
the region of the hilum. The seeds should be rubbed until a small portion of cotyledon
tissue is revealed. Sow the seeds using the rolled towel method. Use two layers of
base paper, and one layer of paper placed on top of the seeds
Results
See table below
Questions
These should encourage reflection/review of what trainees have learnt from the
practical exercise and the associated lecture.
The following questions may be adapted, depending on the species and treatments
tested.
1. Is there evidence that GA promotes the germination of the seeds of
………………..?
2. Explain the observed differences in germination among the three treatments in
experiment 1.
3. Are the seeds of ……………………………….sensitive to alternating
temperature? What is the ecological explanation?
4. Explain the effect of surgical operation in the germination of ………………….
5. Is there evidence that the position of the nip has affected germination in
experiment 2 ?
6. The seeds of …………………… and ………………. have physical dormancy.
True or false?
7. Does KNO 3 promote germination in ………………………?
Supported by
Also supported by

Improving the identification, handling and storage of “difficult” seeds
Results
Rep I Rep II Rep III Rep IV TOTAL
Treatment N A F D N A F D N A F D N A F D N A F D E
Experiment
1 Effect of levels of GA on the germination of …………………….
0mM
0.7mM
10mM
Experiment
2 Effect of alternating temperatures on …………………….
25 o C
30/20 o C
Experiment
3 Effect of surgical treatment on …………………….
Nip 0
Nip 1
Nip 2
Experiment
4 Effect of nipping on the germination of …………………….
Nip 0
Nip 1
Experiment
5 Effect of KNO 3 on the germination of …………………….
0% KNO 3
0.2% KNO 3
Experiment
6 Effect of scarification on the germination of …………………….
Intact
Scarified
Key: N: Normal seedlings A: Abnormal seedlings F: Fresh seeds D: Dead seeds
Supported by Also supported by